"I love our nightly evening chats when I really get to hear what's on your mind. You work hard to get whatever it is you want to achieve, and you have grit and responsibility in spades. I am so damn lucky to be your mother, you beautiful, kind young woman. Thank you for choosing me.
"I adore you to the moon and back a zillion times. I'm sorry you are having this particular birthday during these circumstances, but as always with you, you find the best in everything."
Gwyneth's fans took to the comments section on the post to wish Apple a happy birthday and remarked on how quickly the teenager has grown up.
"Happy happy birthday! How can she be sixteen? She's beautiful!" one fan wrote.
Actress Kate Bosworth commented: "Oh my gosh, I cannot believe she is 16! What a gorgeous, bright spirit."
Another fan said, "Dying that she is 16, what a beautiful tribute from the most kick ass mum to date".
Other fans could not get over the visual similarities between the mother and daughter.
"Happy 16th birthday, you both are like twins!" one Instagram follower comments.
"Gosh she looks like if you and Chris Martin had a baby or something! She's beautiful! Apple doesn't fall far from the tree. Gorgeous," another fan joked.
"She is a young Gwyneth, beautiful girl," another said.
And this fan joked: "I wonder how many times a day you hear 'the apple doesn't falll from from the tree'. She looks so much like you! Happy Birthday Apple."
Gwyneth and Chris Martin "consciously uncoupled" back in 2016. Since their split, both have found love again.
The Oscar-winner is married to producer and writer Brad Falchuk and musician Chris is currently dating his on-and-off girlfriend Dakota Johnson.